1. Field of the Invention
The present invention relates in general to automotive hydraulic brake systems, and more particularly to the automotive hydraulic brake systems of a type that obtains a sufficient pressure reduction performance to a low μ road while restraining a fluid intake resistance of a brake fluid pump.
2. Description of the Related Art
Before describing the automotive hydraulic brake system of the present invention, meaning of the low μ road and the pressure reducing performance will be explained. That is, the low μ road is a road of which surface has a low coefficient of friction and the pressure reduction performance is a performance in effectively reducing the brake fluid pressure for wheel cylinders of the hydraulic brake system, that is needed when the vehicle is braked without skid.
One of the automotive brake systems of the above-mentioned type is described in Japanese Laid-open Patent Application (Tokkai) 2007-238095. In the automotive hydraulic brake system of the publication, there is employed an internal reservoir that temporarily reserves a brake fluid from wheel cylinders for adjusting a fluid pressure that is applied from a master cylinder to an intake port of a fluid pump. The internal reservoir shown by the publication comprises a larger main case, a smaller auxiliary case, an apertured valve seat portion through which the main and auxiliary cases are connected, a piston slidably disposed in the main case, a biasing spring installed in the main case to bias the piston toward the auxiliary case, a pin connected to the piston and extending to the auxiliary case through the apertured valve seat portion, a ball (or valve body) placed in the auxiliary case and contactable to a leading end of the pin to move therewith. An operation chamber of the main case is connected to an inlet port of a rotary pump and the auxiliary case is connected to a downstream side of a brake fluid circuit.